The present invention is directed to automatic stacking machines, and in particular, to self-contained machines for stacking elongate, stackable workpieces.
Automatic stacking machines are well known in the prior art. Extended arm-type hoisting stackers are used in the wood products industry to stack processed workpieces for shipping. In the operation of an extended arm-type hoisting stacker, processed workpieces are moved along an inclined surface and delivered to the extended arms of the stacker. The individual workpieces are collected on the extended stacker arms until a single layer of a predetermined number of workpieces is accumulated. The single layer of workpieces on the extended stacker arms are then moved to a position over the workpiece stack being formed. The stacker arms are then retracted from beneath the single layer of workpieces, depositing same on top of the formed stack which is supported in a raised position by a separate scissor-type indexable table. The stacker arms return to their initial extended position to receive further processed workpieces and to form another single layer. The stack is then lowered by indexing the scissor-type table to a position for receiving the next single layer. The above-described stacking sequence is repeated until a formed stack is completed on the scissor table. At that time the formed stack is removed from the scissor table, and the formation of a new stack is commenced. Extended-type arm stackers are large units which are permanently installed in, for example, a wood remanufacturing facility. They also require a substantial amount of floor space since the workpieces are raised to stack height along the inclined surface of the extended arm. The stack under formation is not contained within the limits defined by the length of the stacker portion of the machine. Instead, there must be sufficient room outside the periphery of the stacker itself for the extended arm to deliver the workpieces in stacked line to the formed stack. For these reasons, arm-type stackers are not easily retrofitted to an existing processing facility, particularly within confined stacking and loading areas. Extended arm-type stackers are not well-suited to a facility which produces a variety of different sized workpieces. They are limited to a relatively narrow size range of workpieces and do not accommodate variations in handling requirements for different workpieces prior to stacking. They also do not function in situations where there are variations in the process which result in the workpieces being delivered for stacking to different locations in the facility. Finally, extended arm-type stackers are stationary and cannot be readily moved from place-to-place within the manufacturing facility.
A variation of the extended arm-type stacker uses a moving continuous chain with attached T-shaped brackets to vertically lift the workpieces and place them on stacking arms. When a single layer of workpieces has been formed on the stacking arms, the workpiece feed process stops, and the arms are moved downward to floor level. Typically, the single layer of workpieces on the stacking arms is positioned over a pallet. The arms are then retracted, depositing a single work piece layer on the pallet. This retraction step is conducted by moving the stacking arms laterally out of the way of the workpiece layer which requires an amount of free, unusable space being available alongside the stacker to accommodate the stacking arms which is a least equal the length of the stacker arms. The arms are then moved to an extended position and then vertically upward to receive another layer of workpieces. When the next layer of workpieces is deposited on the stacking arms, they are again moved downward, as described above, and the workpiece layer stacked atop the prior deposited layer. These steps are repeated until the stack is completed, at which time the pallet is removed and a new stack is begun. Stack formation is accomplished by stacking the workpieces beginning at the bottom of the stacking machine and working up toward the top of the machine. There is substantial time lost each time the stacker arms with the layer of workpieces thereon are lowered from the upper loading position to the lower stack formation position in bottom-to-top stack formation. Moving chain arm-type stackers also causes many of the same problems of extended arm-type stackers. They are large, permanently installed units which cannot be readily moved from place-to-place. They require a large amount of floor space since the stacker arm during formation is not contained within the confines of the periphery of the stacker but retracts to a lateral position alongside the machine. For these reasons, moving chain arm-type stackers are also not easily retrofitted to an existing processing facility. Moving chain arm-type stackers are also not well-suited to a facility which produces a variety of workpieces. They are further limited to a relatively narrow size range of workpieces which can be engaged by the T-type brackets and do not accommodate variations in handling requirements for different workpieces prior to stacking, nor variations in the process which result in the workpieces being delivered for stacking to different locations in the facility.
A need therefore exists for an automatic stacker which can stack a wide variety of sizes of elongated workpieces, which can receive workpieces in a variety of entry feed orientations, which is compact and self-contained for conserving valuable floor space, which is readily retrofittable to existing facilities, and which is portable to and is readily movable to various locations within a facility.